Dictionary.net

A non-covalently bound subunit of the glycoprotein hormones TSH; FOLLICLE STIMULATING HORMONE; LH; and HCG which originates in the anterior pituitary gland and placenta. This subunit is virtually identical in structure and indistinguishable by radioimmunoassay in all of the above glycoproteins. It is present in both men and women, but is elevated in postmenopausal women and in patients with hypothyroidism, uremia and malignant tumors. The alpha subunit may be involved directly in recognition of certain receptors.